I'm working on a story dealing with changelings, and I'm running into a bit of trouble figuring out how I should identify them in the text during a certain scene.

There are three disguised changelings involved, who we will refer to as 'Buggy', 'Mimic', and 'Echo'. The story, at this point, is following Echo's perspective.

Just prior to this scene, Buggy has been acting irrationally, to the point of requiring 'Mimic' to temporarily shut down her mind. (Picture it as being knocked unconscious, but mentally instead of physically.) Mimic then has to manipulate Buggy's body (not quite hivemind effect, but similar), so as to keep anyone else around from realizing anything's going wrong.

How should I tag Buggy's actions and speech when Mimic is in control of her? It's not really Buggy acting or speaking, after all, and as Buggy is in control of herself at other points in the story I feel that I have to set up some way to differentiate between them, but just saying 'Mimic' instead could cause confusion if both characters are in the same scene, which -will- be happening.

Any suggestions?

5615343
Buggy's body. Buggy's body turned to the right, or "I like that idea," Buggy's body said. Specifying that it's the body--maybe even calling it "it" every now and then--would suggest the individual intelligence isn't present for it to be Buggy herself.

You could try using italics for the puppeting action. For the rest of the story just use normal text when Buggy is in control. For example it could go something like this:
Mimic waved at the ponies; Buggy waved with her, almost but not quite in sync. Echo waved too. It made her feel awkward.

What Mind's Eye said, or, if Mimic is the POV character in such a scene, "I turned Buggy's body to the right" or «I had Buggy say, "Yes, boss!"». (or, with 3rd-person omniscient, "Mimic turned Buggy's body to the right.")

If it's a 3rd-person limited POV who is not in on it, just say that Buggy did it, but showing whatever apparent flaws of remote-control exist, if any.

5615343 I dunno, provided that the reader is made well aware of what's going on you could probably play it pretty much as normal, with an occasional reminder in the form of descriptions of Mimic needing to make Buggy react to certain things, etc.

Yeah, write the dialogue and actions normally, *except* try to create a disconnect. For example, instead of 'Buggy walked to the left' say 'Buggy was made to walk to the left' or something like that. 'Buggy's mouth opened and said,' etc. Make the dialogue tags and actions disconnected like that, make them written strangely, unnatural. In addition to explaining the situation of what's going on beforehand, oddly written action and dialogue tags that imply (on their own) that Buggy isn't the one doing things that Buggy is doing, will help drive the idea home.